Movable mirror device

ABSTRACT

A movable mirror device is provided as a unitary device with a position sensor and an analog-to-digital converter included in the unitary device.

CROSS-REFERENCE TO RELATED APPLICATION DATA

This patent application is a continuation of U.S. patent applicationSer. No. 14/934,270, filed on Nov. 6, 2015, the contents of which areincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present application relates to movable mirror devices, and to laserscanners using such movable mirror devices as scanning mirrors.

BACKGROUND

In various applications, an area, for example an area of a sample to beexamined, needs to be scanned with a light beam. For instance, in laserscanning microscopy (LSM), where a sample is scanned with a laser beam,and light emitted by the sample in response to being irradiated with thelaser beam is detected. For scanning, the laser beam is directed at oneor more tiltable mirrors, also referred to as scanning mirrors. Bytilting the one or more mirrors, a position of the laser beam on thesample may be adjusted. For example, in some applications a singlemirror tiltable about two perpendicular axes may be used. In otherimplementations, two successive mirrors each being tiltable only aboutone axis, the axes of the two mirrors being not collinear with eachother, for example perpendicular to each other, may be used.

In many applications, additionally position sensors are employed todetermine a current position of the one or more movable mirrors. Variouskinds of such position sensors may be used.

Movable mirrors may for example be manufactured asmicroelectromechanical systems (MEMS). In such microelectromechanicalsystems, for example the parts actuating the mirror (i.e. moving themirror), and in some cases also the mirror itself may be formed in asemiconductor wafer, for example a silicon wafer, together withelectronic components.

Conventionally, such movable mirrors are provided as a device togetherwith analog amplifiers amplifying one or more analog signals from aposition sensitive device like a four quadrant diode. The amplifiedanalog signals are then transmitted to some target hardware for examplevia a suitable connection (for example with a plug-in connector). In thetarget hardware, the amplified analog signals provided by the movablemirror device may then be digitized and further processed, for exampleto determine the position of the mirror and to control the mirroraccordingly.

This approach may be disadvantageous in term of calibration needed forthe mirror device and regarding flexibility. For example, a certaincalibration may only be valid for a certain combination of scanningdevice and target hardware, such that when the scanning device needs tobe replaced, a recalibration becomes necessary. Furthermore, because ofthe calibration being necessary, it is difficult for a singleconventional movable mirror device to interact with different targethardwares.

SUMMARY

In some embodiments, a movable mirror device is provided which isimplemented as a unitary device. The unitary device may comprise aposition sensor device adapted to capture a position of a movablemirror, a processing device and at least one analog-to-digital converteradapted to convert an analog signal received directly or indirectly fromthe position sensitive device to a digital signal. The processingcircuit in some embodiments may further implement one or more functionsfor processing the digital signals like filtering, correcting ordetermining a position of a movable mirror based on the signals.

The above summary is only intended to give an overview over somefeatures of some embodiments and is not to be construed as limiting inany way. Other embodiments may include other features than the onesdescribed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a laser scanning microscope as an exampleapplication environment for embodiments.

FIG. 2 is a block diagram of a conventional device.

FIG. 3 is a block diagram of a movable mirror device according to anembodiment.

FIG. 4 is a more detailed block diagram of a movable mirror deviceaccording to some embodiments.

FIG. 5 is a diagram illustrating a data format usable in someembodiments.

FIGS. 6 and 7 are diagrams illustrating synchronization mechanismsaccording to some embodiments.

FIGS. 8 and 9 are diagrams illustrating systems according to someembodiments.

FIG. 10 is a flowchart illustrating operation of a processing deviceusable in some embodiments.

DETAILED DESCRIPTION

In the following, various embodiments will be described in detailreferring to the attached drawings. These embodiments are given by wayof example only and are not to be construed as limiting. For example,while some embodiments may be described as comprising a plurality offeatures or elements, this is not to be construed as indicating that allthese features or elements are necessary for an implementation. Instead,in other implementations or embodiments, some of the features orelements described may be omitted and/or may be replaced by alternativefeatures or elements. Furthermore, in addition to the featuresexplicitly described and shown in the drawings, additional features orelements, for example features or elements commonly used in movablemirror devices or laser scanning devices, may be provided withoutdeparting from the scope of the present application.

Features or elements from various embodiments may be combined to formfurther embodiments. Modifications or variations described with respectto one of the embodiments may also be applied to other embodiments.

In some embodiments, movable mirror devices are provided as unitarydevices. A unitary device in the context of the present application is adevice provided as a single unit. A unitary device may be a device whereall components of the device are mounted or otherwise fixed to a singleprinted circuit board (PCB) or a plurality of printed circuit boardsfixedly connected to each other; and/or a device where all components ofthe unitary device are provided in a single housing; and/or; a devicewhere all components of the unitary device have a fixed spatialrelationship with each other. In some cases, the unitary device may alsobe referred to as a package.

Movable mirror devices according to some embodiments may for example beused as scanning mirrors in laser scanner devices, for example laserscanning microscopes. To illustrate, FIG. 1 shows a schematic diagram ofa laser scanning microscope where embodiments of movable mirror devicesmay be employed. FIG. 1 is only a simplified representation, and variouscomponents of conventional scanning mirror devices like pinholes mayadditionally be employed. However, it is emphasized that the use ofmovable mirror devices of embodiments is not limited to scanningapplications like laser scanning microscopy applications, but may beused in various applications where a light beam (including for exampleinfrared or ultraviolet light beams) is to be directed in a variablemanner by moving a movable mirror. Other example applications includefor example exposing printed circuit boards (PCBs) in photolithographyprocesses or writing of structures on an object by means of a laserbeam, but are not limited thereto.

In the laser scanning microscope system of FIG. 1, a laser 10 generatesa laser beam 11. Laser beam 11 is directed to a scanning mirror 12.Scanning mirror 12 or parts thereof may be implemented as amicroelectromechanical system (MEMS), for example a silicon basedmicroelectromechanical system. Scanning mirror 12 in the example of FIG.1 is tiltable about two perpendicular axes controlled by a controller14. By tilting mirror 12, laser beam 11 may scan a sample 15.

Light emitted from sample 15 in response to being irradiated by laserbeam 11 is captured in a time resolved manner by a photomultiplier tube(PMT) 16. By capturing the light emission from sample 15 in a timeresolved manner, a current signal output by photomultiplier tube 16 maybe associated with a corresponding current scanning position of laserbeam 11 on sample 15. The current scanning position may be obtainedbased on a signal from a position sensor 13 measuring the position ofscanning mirror 12. Based on the signal from photomultiplier tube 16, animage 17 of the sample is calculated. The above laser scanningmicroscopy approach may be implemented in any manner conventionallyknown in the art.

The system of FIG. 1 further comprises a position sensor including inthe example of FIG. 1, a position sensitive device 13, for example afour quadrant diode. The position sensor further comprises a lightsource. Light from the light source like a light emitting diode (LED) isdirected to a backside of scanning mirror 12. Backside in this contextrefers to the side of scanning mirror 12 which faces away from laser 10,while frontside refers to the side onto which laser beam 11 is directed.Light from the light source is reflected from the backside of mirror 12onto position sensitive device 13. When scanning mirror 12 is tiltedabout its axes, the spot onto which light from the light source isreflected on position sensitive device 13 moves, thus allowing adetection of the movement and position of scanning mirror 12. Based onthe position measured by position sensitive device 13 and on a controlsignal, a controller 14 controls the position of scanning mirror 12, forexample to allow a scanning of sample 15. Other position sensors mayalso be used.

Scanning mirror 12 as well as position sensitive device 13 inembodiments, may be provided in a unitary device or package as a movablemirror device according to some embodiments. In case of an MEMS beingused for scanning mirror 12 this unitary device may also be referred toas MEMS unit.

Controller 14 in some cases may be implemented as a computer device andmay for example be connected to the MEMS unit via a cable or via awireless connection.

For better understanding of the embodiments which will follow, FIG. 2illustrates a conventional implementation of an MEMS unit as acomparative example for the embodiments which will be discussed later.

FIG. 2 illustrates a conventional MEMS unit 20 as a comparative examplewhich comprises a quadrant diode 21 as a position sensitive device, alight emitting diode (not explicitly shown), and which embodiment may bemodified according to the present disclosure to incorporate a MEMSmovable mirror (not shown in FIG. 2, for example mirror 12 of FIG. 1).Furthermore, MEMS unit 20 comprises operational amplifiers 22 a, 22 b,22 c and 22 d, collectively referred to as operational amplifiers 22hereinafter. Each of amplifiers 22 is associated with one of thequadrants of four quadrant diode 21 and amplifies a signal from therespective quadrant. The amplified signals from amplifiers 22 a-22 d,which are analog signals, are transmitted to some target hardware 23 forfurther processing. This transmission may for example be via a cableconnection, for example using a plug-in cable, or via a wirelessconnection. Target hardware 23 is therefore hardware distinct from MEMSunit in the comparative example of FIG. 2.

In target hardware 23, the analog signals received from MEMS unit 20 maybe amplified via amplifiers 24 a-24 d (collectively referred to asamplifiers 24) and converted to digital signals via analog-to-digitalconverters (ADCs) 25 a-25 d (collectively referred to asanalog-to-digital converters 25).

The digital output signals of analog-to digital converters 25 areprovided to a processing device 26, which performs various kinds ofprocessing 27. For example, processing 27 may comprise digitalfiltering, correction (for example a dark current correction), anddetermining a position of the movable mirror based on the signals fromADCs 25. The determination of the position may be based on values storedin a lookup table (LUT) 28. Values in lookup table 28 may for example bedetermined during a calibration process, where a mirror of MEMS unit 20is brought into predefined positions and corresponding signals fromquadrant diode 21 are measured. The correlation between measured signalsand positions may then be stored in lookup table 28.

Processing device 26 may be implemented as a specially configuredcomputational device, for example using a processor like a digitalsignal processor (DSP), a microcontroller (μC), or also fixed(hard-wired) logic provided e.g. as an FPGA (field programmable gatearray) and combinations thereof together with any corresponding softwareto implement the special purpose functionality described herein.

The thus determined position of the movable mirror may then be output asindicated by an arrow 29 to further units, devices or components, andmay for example be used in a controller like controller 14 to controlmovement of a mirror like mirror 12.

In the comparative example of FIG. 2, the content of the lookup table 28has to be updated when for example MEMS unit 20 or target hardware 23 isreplaced. In particular, both manufacturing tolerances of MEMS unit 20and manufacturing tolerances in target hardware 23 (leading for exampleto differences in analog-to-digital converter behavior) influence lookuptable 28. Therefore, a recalibration of the system is for examplenecessary when MEMS unit 20 is exchanged (for example due to faults).

FIG. 3 illustrates a schematic block diagram of a movable mirror device30 according to an embodiment. Movable mirror device 30 is provided as aunitary device. Movable mirror device 30 of the embodiment of FIG. 3comprises a movable mirror 32, and a position sensor 31 associated withmovable mirror 32. Movable mirror 32 may for example comprise amicroelectromechanical system. Position sensor 31 may comprise aposition sensitive device, for example a quadrant diode, and a lightsource as discussed above. Other position sensors may also be used.Furthermore, movable mirror device 30 comprises a controller 33 as anexample for a processing device. Controller 33 may comprise a processorlike a digital signal processor (DSP), a general purpose processor,hardwired logic, for example an FPGA (field programmable gate array)and/or memories storing software to perform functions discussed furtherbelow. Furthermore, controller 33 comprises one or moreanalog-to-digital converters 34 to convert one or more analog signalsfrom position sensor 31 to digital values, which then may be furtherprocessed by controller 33. Therefore, in contrast to the comparativeexample of FIG. 2, in the embodiment of FIG. 3 the analog-to-digitalconverter 34 is provided with the unitary movable mirror device 30.

Controller 33 may in some embodiments determine a position of movablemirror 32 based on the digitized signal from position sensor 31. Forexample, controller 33 may comprise a lookup table. Such a lookup tablemay be obtained by calibration for example at a manufacturer whomanufactures movable mirror device 30. Such calibration may for examplecomprise bringing the movable mirror to predefined positions andmeasuring the signal of position sensor 31, and storing the positiontogether with the signal. For calibration, specific parameters like alookup table may then be programmed via an interface, for example aninterface 35 or an additional interface for calibration purposes, forexample a serial interface. As movable mirror device 30 is a unitarydevice, the calibration may be performed in advance at a manufacturer,and device 30 may be easily replaced without the need for arecalibration. Controller 33 then may communicate the position tofurther devices, for example a target hardware, via an interface 35. Insome embodiments, as will be explained later in more detail, interface35 may be a bus interface.

In some embodiments, controller 33 may additionally control movablemirror 32 based on a control signal received via interface 35. Signalsoutput by controller 33 to control movable mirror 32 may be amplified bya high voltage amplifier (HV-amplifier) in case movable mirror 32requires high voltage signals, as it is often the case for MEMS mirrors.In other embodiments, the position of movable mirror 32 may becontrolled directly via signals, e.g. signals having appropriate voltagelevels, provided to movable mirror device 30 via interface 35 or anyother connector, without involving controller 33.

In some embodiments, besides determining a position of movable mirror 32based on a signal from position sensor 31, controller 33 may perform oneor more further functions. For example, controller 33 besides thedetermined position may select signal values at internal nodes ofmovable mirror device 30 to be transmitted via interface 35. In someimplementations, an output signal of ADC 34 or any other internal signalavailable to controller 33 may be transmitted via interface 35. In someembodiments, such signal values may be transmitted upon a requestreceived via interface 35. Controller 33 may in some embodiments alsoperform filtering or correcting functions. In some embodiments,controller 33 may also assist in calibrating or determining otherparameters of movable mirror device 30, for example determiningcoefficients of a filter for dark current suppression. Other functionsmay be provided in a target hardware coupled to movable mirror device30, for example further functions for calibration or parametrization ofdevice 30, further processing of position data or signals from systemnodes or synchronizing transmission from movable mirror device 30.Examples for such synchronization will be discussed further below.

As mentioned, control of the movable mirror 32 may be performed in anyconventional manner. In the embodiments which will be described next,therefore, the movable mirror and control thereof will not be discussedin any further detail.

FIG. 4 illustrates a further embodiment of a movable mirror device, inthe example embodiment of FIG. 4 an MEMS unit 40, according to someembodiments. In the embodiment of FIG. 4, as discussed above, themovable mirror itself, which in this case may be implemented using amicroelectromechanical system, is omitted and may be operated in anyconventional manner. MEMS unit 40 in the embodiment of FIG. 4 isimplemented as a unitary device.

MEMS unit 40 of FIG. 4 comprises a quadrant diode 41 and a lightemitting diode (LED) 42 serving as an example for a position sensor. Inoperation, light emitting diode 42 illuminates a backside of a movablemirror, and light from light emitting diode 42 is reflected from thebackside of the movable mirror onto four quadrant diode 41. A movementof movable mirror 41 (tilting about its axes) moves a reflection spot oflight emitting diode 42 on four quadrant diode 41, which changes outputsignals of four quadrant diode 41.

The output signals of four quadrant diode 41 are provided to operationalamplifiers 45 a-45 d, collectively referred to as operational amplifiers45, for amplification.

In other embodiments, other kind of position sensors may be used, andone or more output signals of such position sensors may be provided tooperational amplifiers if amplification is required. For example,instead of four quadrant diode 41, an extended p-i-n semiconductorstructure may be used as position sensitive device to detect lightreflected from the movable mirror. In other embodiments, a tilting angleof movable mirror 41 may be sensed via a capacitance change of thebackside of mirror 41 or a comb structure associated with mirror 41. Inyet other embodiments, the position of mirror 41 may be sensed using aresistive bridge structure sensing a torsion of a spring elementassociated with mirror 41 or a bending of a bending element associatedwith mirror 41, the spring or bending element changing its resistancewith torsion or bending, respectively.

Output signals from operational amplifiers 45, which are analogamplified signals, are provided to analog-to-digital converters 46A-46D,respectively, to be converted into digital format. The thus generateddigital signals are processed by a processing device 47. Processingdevice 47 may for example comprise a digital signal processor, a generalpurpose processor, hardwired logic or any other suitable components orcircuits to perform the processing described below. For example,processing unit 47 may perform filtering of the signals fromanalog-to-digital converters 46, may correct them (for example to filterout or remove a dark current, i.e. a signal generated by four quadrantdiode 41 even when it is not illuminated, or for offset correction). Adark current correction may for example be performed by measuring thedark current in a calibration (with light emitting diode 42 turned off)and then subtracting a digital representation of the measured darkcurrent from signals measured during actual operation.

Furthermore, processing unit 47 may determine a position of the movablemirror based on the signal from ADCs 46 for example using a lookup table48, essentially as explained above. In other embodiments, a polynomialfit between some predefined values may be used instead of a (full)lookup table. The position may be transmitted via a data bus 411 to atarget hardware. The target hardware may process or use the positionfurther, for example to control the movable mirror or to correlate theposition to a signal obtained from a sample, as explained with referenceto FIG. 1.

Furthermore, processing device 47 may also transmit other signalscorresponding to signal values at some system nodes of MEMS unit 40 viadata bus 411. For example, the outputs of analog to digital converters46 (four values in the example of FIG. 4) may be transmitted withoutfurther processing. Also, output values of filter functions or valuesafter dark current correction may be transmitted. The position may beprovided as normalized values or as non-normalized values.

The above-mentioned functionality of processing device 47 is furtherillustrated in FIG. 10, which is a flowchart illustrating an example forprocessing in processing device 47. While FIG. 10 illustrates theprocessing as a series of acts or events, the order in which these actsor events are illustrated and described is not to be construed aslimiting.

At 100 in FIG. 10, the processing device (for example processing device47 of FIG. 3) receive digital values representative of signals from aposition sensor (for example digital signals from analog-to-digitalconverters 46).

At 101, the processing device performs a digital filtering, for exampleat low pass filtering, high pass filtering, bandpass filtering, noisefiltering etc.

At 102, the processing device performs a dark current correction. Forexample, previously stored correction values may be subtracted from thefiltered digital values after 101.

At 103, the processing device performs an offset correction. Similar to102, for example previously stored value may be added to or subtractedfrom the digital values after the dark current correction at 102.

At 104, the position of the movable mirror is calculated based on theoffset corrected values after 103. For example, using a lookup tableposition values corresponding to the digital values may be read out ofthe lookup table, or an interpolation may be performed.

It has to be noted that depending on the implementation, only some ofthe acts or events described with respect to FIG. 10 may be implementedin a processing device. Moreover, the act or events may be performed ina different order than shown. Other implementations are also possible.

Furthermore, MEMS unit 40 in the embodiment of FIG. 4 comprises an LEDcontroller for controlling light emitting diode 42. While LED controller410 is depicted as a separate entity in FIG. 4, the functions of LEDcontroller 410 described in the following may also be performed byprocessing unit 47. LED controller 410 may control light emitting diode42 for example to ensure a constant illumination intensity over time.

For example, when operating MEMS unit 40, due to heating and aging anintensity (for example brightness) of light emitting diode 42 andtherefore of a reflected spot on quadrant diode 41 may change (e.g.decrease), which changes the output signals of quadrant diode 41.Therefore, LED controller 410 in some embodiments may implement acontrol scheme for controlling the intensity of light emitting diode 42,for example by regulating a drive current accordingly. For example, LEDcontroller 410 may implement a PI (proportional integral) controller.The controlling may be performed for example before each scanning duringeach scanning.

For example, for controlling in an embodiment during a calibration a sumsignal of all four quadrants (e.g. a sum of the output signals ofanalog-to-digital converters 46) may be calculated and stored in amemory like a flash memory as a target value. During this measurement,in an embodiment the mirror is in a rest position, which may help todisregard changes in voltages for controlling the mirror. Before eachscan, during an initialization, in embodiments the mirror again isbrought to its rest position, and the sum signal of all four quadrantsis obtained. Based on this sum signal and the target value previouslystored, a current supplying light emitting diode 42 may be controlledand adjusted, for example using a PI control scheme. In embodiments, assoon as the difference between the current sum signal and the storedtarget value is within a predetermined tolerance range, initializationmay be ended and scanning may start.

In other embodiments, a current supplying LED 42 may be controlledduring scanning. For such an embodiment, the above-mentioned sum signalmay for example be stored as a target value for each position of themovable mirror during an initial calibration. During scanning, for eachscanning position or in regular or irregular intervals the sum signal isagain formed and compared to the respective target value for therespective position, and a controlling of the LED current is performedas mentioned above.

As mentioned above, processing unit 47 may transmit data via data bus411. Furthermore, in the embodiment of FIG. 4 a command bus 412 isprovided, via which an external entity, for example the alreadymentioned target hardware, may control MEMS unit 40 for example toprovide desired data of some internal nodes (like the ones mentionedabove, for example ADC output values). Furthermore, a synchronizationsignal 413 may be received to synchronize transmitting of data via databus 411, which will be explained below in further detail. For handlingcommands via the command bus and synchronization, a system controller 49is indicated in FIG. 4, which may again be implemented using processingunit 47.

The MEMS unit 40 may be provided in different configurations fordifferent embodiments. For example, as indicated by a dashed line 43,all components within dashed line 43 including operational amplifiers 45may be provided as a single system on chip (SOC) integrating bothdigital components and the analog amplifiers 45. In another embodiment,as indicated by a dashed line 44, operational amplifiers 45 may beprovided as discrete components and the components within dashed line 44may be provided for example as a single microcontroller including analogto digital converters 46, or any other suitable piece of hardware. Inyet another embodiment, also analog-to-digital converters 46 may beprovided as discrete elements, such that a purely digital processingdevice may be used. In all of the above cases, all components of MEMSunit 40 are provided in a unitary device, for example mounted to asingle printed circuit board or a combination of printed circuit boardscoupled with each other in a fixed manner.

Next, functions of data bus 411, command bus 412 and synchronizationinput 413 will be explained in some more detail referring to FIGS. 5-7.

Data to be sent, for example position data or data regarding internalnodes as described above, may be sent via data bus 411 to one targethardware or a plurality of target hardwares. In some embodiments, aspecific target hardware may be selected via an identification (ID)number or any other identification, which may precede payload data (e.g.position data). Each bit of such an ID number may represent a specifictarget hardware. For example, by setting more than one bit, the data maybe sent to more than one target hardware. FIG. 5 shows an illustrativedata transmission cycle via data bus 411. In the example of FIG. 5,which is given for illustration purposes only, a four bit transmissionis used. The bits are labeled data bus(0) to data bus(3) in FIG. 5.

First, a four bit ID (ID-BIT 0 to ID BIT 3) is sent. Each bit maycorrespond to a target hardware. In the example of FIG. 5, thereforefour different target hardware entities may be addressed. In otherembodiments, other bit widths may be used, and/or other codings for theID may be used. Therefore, the illustrative data transmission cycle ofFIG. 5 is merely a non-limiting example for illustration purposes, andother kinds of data transmission may also be used.

Following the ID number, in the example of FIG. 5 position data for anx-axis position (for example tilting about an x-axis of the movablemirror) and position data for a y-axis position (e.g. tilting about ay-axis) is transmitted. Each position (x and y) is represented as a 16bit value in the example of FIG. 5, thus needing four 4 bit values fortransmission. As mentioned, the transmission cycle of FIG. 5 serves onlyas an example. In case values of some internal nodes (for example outputof values of ADCs) are to be transmitted additionally, these may forexample be transmitted following the position data.

Next, the function of the command bus 412 will be explained in some moredetail. The command bus, as mentioned, may be used to request or selectin values of internal system nodes to be sent via the data bus.

Furthermore, command bus 412 may be used to program one or more systemparameters of MEMS unit 40 and/or to control some additional functionsof MEMS unit 40. Some non-limiting examples for control via command bus412 will be explained below:

-   -   A sampling rate of analog-to-digital converters 46 may be        adjusted via command bus 412.    -   Lookup table 48 may be updated, or other coefficients like        filter coefficients may be provided via command bus 412.    -   Version numbers or internal system variables may be provided.    -   Parameters of a movable mirror used, for example a type of        movable mirror or parameters of the movable mirrors, may be set.    -   A regulation of a current supplying light emitting diode 42 (for        example as explained for LED controller 410) may be activated        and deactivated.

The above are only non-limiting examples, and in other embodiments onlysome of these functions, or alternative functions, may be implementedusing command bus 412.

Command bus 412 may for example be a serial bus, as a serial bus orserial interface is comparatively easy to implement and the functionsperformed via command bus 412 are in many embodiments not critical.However, other kinds of busses or interfaces may also be used.

Next, synchronization input 413 (for example via a sync signal receivedat input 413) will be discussed. The sync signal may be provided via aseparate input as shown in FIG. 4, but in other embodiments may forexample be provided via command bus 412. In some embodiments, via a syncsignal, an external hardware (for example the above mentioned targethardware) may start synchronizing data output via data bus 411 and/orsampling times of analog-to-digital converters 46 at or to desiredpoints in time. For example, in some embodiments more than one mirrormay be used, and in such a case position signals indicating the positionof the different mirrors, for which different MEMS units 40 may beprovided, have to be processed in a coordinated manner. In suchapplications, it may be desirable that the sampling points andtransmission of position data is performed at least essentially at thesame time in different MEMS units 40. On the other hand, as the MEMSunits 40 are different unitary devices, they may use different internalclockings, which may not be synchronized and/or which may losesynchronization over time due to slight differences between clocks. Forexample, at low sampling rates time deviations between position signalsmight lead to errors in controlling the mirrors in some cases. Forsynchronization, a synchronization signal may for example be sent to allinvolved MEMS units at the same time.

In some embodiments, a signal at the synchronization input 413 with afirst logic level (for example high) indicates that a synchronization isto be performed, while a signal at another logic level (for example low)does not influence operation of MEMS unit 40. In case a sync signal withthe first logic level (for example high) is applied, in embodiments acurrent transmission of position data may be finished normally, but nonew transmission is initiated as long as the synchronization signal isat the first logic level. The same may apply to sampling. In someembodiments, such a synchronization signal (set to the first logiclevel) may occur during three different phases of signal processing inMEMS unit 40. This is illustrated in FIG. 6.

In FIG. 6, a processing cycle comprises a calculation of position(calcpos), followed by a transmission of data (send), followed by a waitphase (wait). Each cycle of these three phases is initiated by aninterrupt, as marked by arrows. The first phase of calculating theposition may comprise sampling the data by analog-to-digital converters46 and performing a conversion to position data e.g. via a lookup table,as explained above. The send phase may comprise transmitting theposition data via data bus 411. The wait phase separates this cycle fromthe next cycle. As indicated by arrows 60, 61 and 62, a synchronizationevent (setting the synchronization signal to the first logic level) mayoccur in each of the three phases. In some embodiments, irrespective ofthe phase, the current cycle is finished, but no new cycle is started aslong as the synchronization signal is at the first logic level. In otherembodiments, for example only if the synchronization occurs during thetransmission (arrow 61), the sending is finished and otherwise the cycleis aborted. Other schemes may also be used.

In some embodiments, as soon as the synchronization signal goes to thesecond logic level again, the cycle is started with the positioncalculation calcpos.

FIG. 7 illustrates such a synchronization for three MEMS unit like MEMSunits 40 of FIG. 4 or movable mirror device 30 of FIG. 3. A lineMEMS_0_DATA illustrates data transmission from a MEMS unit #0,MEMS_1_DATA illustrates data transmission from MEMS unit #1, andMEMS_2_DATA illustrates data transmission from an MEMS unit #2. In aline labeled “send”, some points in time where calculated data units aresent are marked. As can be seen, at the beginning (left side of FIG. 7)the data transmissions from the various MEMS units are not insynchronization with each other. Then, a sync pulse is applied (firstline in FIG. 7), e.g. a value of the sync signal goes from low to highto start the pulse and then to low again to end the pulse. A length ofthe sync pulse may be longer than a send time such that during the syncpulse sending of data in progress may be terminated, in particularlonger than the time for a complete cycle including analog-to-digitalconversion, position calculation and sending of data. With a fallingedge of the sync pulse, as indicated by an arrow 70, in an embodimentsampling of the analog-to-digital converters 46 starts. Therefore, thecycle illustrated in FIG. 6 is started in all MEMS units. Therefore,after the synchronization the sending of data occurs essentially at thesame time in all MEMS units. For example, when the sync pulse asserts ahigh value, a last or current transmission of position data is completedin all MEMS units, and then a wait state is assumed until the sync pulsegoes back to a low value. In some embodiments, such a synchronizationmay be performed in regular or irregular intervals, for example whentransmission from various MEMS units differ by more than a predeterminedvalue.

The signals and formats illustrated in FIGS. 5 to 7 serve only forfurther illustration, and in other embodiments other formats may be useddepending on a particular implementation.

MEMS units and movable mirror devices as defined above may for examplebe used in laser scanning applications, as illustrated in FIG. 1, butare not limited thereto. More than one MEMS unit and/or more than onetarget hardware may be used, as already mentioned. To illustrate thisfurther, FIGS. 8 and 9 show two different, non-limited applicationscenarios.

FIG. 8 illustrates a scenario where a single MEMS unit 80 is coupled tothree target entities 81, 82 and 83. Target hardware entities may beselected as receiving data via a data bus for example via theiridentifications, as explained with respect to FIG. 5. In the exampleapplication of FIG. 8, all target hardware entities 81 to 83 are coupledwith MEMS unit 80 via a command bus and a data bus. Synchronization asexplained above is performed only by target hardware 81. Therefore, inthis case adjustment and control of MEMS unit 80 apart fromsynchronization may be performed by each of target hardware entities to83.

FIG. 9 illustrates a further application scenario where three MEMS units91, 92 and 93 are coupled with three target hardware entities 94, 95 and96 via a command bus and data busses. Synchronization is performed againonly by target hardware 94. Each MEMS unit can, by choosing an ID,select which target hardware entities 94 to 96 should receive processfor example position data.

The bus structures as illustrated above are only examples, and other busstructures may also be used. For example, the various functions (databus, command bus and synchronization) may also be implemented on asingle physical bus, for example using time division duplexing (TDD),frequency division duplexing (FDD) or any other duplexing ormultiplexing technics commonly employed for bus systems. Instead of bussystems, in other embodiments point-to-point connections may be used.

MEMS units as discussed herein may have one or more of the followingadvantages in some embodiments. In other embodiments, the MEMS units mayhave other properties.

-   -   In some embodiments, the MEMS units may be coupled in an easy        manner with various components of target hardware and directly        may deliver position data. Therefore, no calibration due to some        relevant components being in the target hardware and others        being in the MEMS unit are necessary.    -   Position data may be provided to different target hardware        entities, as illustrated for example in FIGS. 8 and 9.    -   No separate analog-to-digital converters have to be provided on        the target hardware.    -   In some embodiments, a signal quality may be increased, as for        example analog signals of operational amplifiers do not have to        be transmitted via longer distances to a target hardware.        Sending digital data may be more robust against noise sources.    -   A control of a LED current may be easily implemented.    -   In some embodiments, information and parameters may be stored in        a memory of a processing unit, for example a flash memory.    -   In embodiments where a sampling rate is programmable, various        mirror types with different mechanical properties may be        supported, for example in case of resonance scanners having        different resonance frequencies.    -   In some embodiments, a synchronization signal may enable a        synchronization between various MEMS units.    -   Control of the MEMS units may be easily implemented via a serial        interface.

The above-described embodiments serve only as an example, and variationsand modifications are apparent to persons skilled in the art andconsidered to be within the scope of this disclosure.

What is claimed is:
 1. A movable mirror device, comprising: a movablemirror, a position sensor measuring a position of the movable mirror andoutputting at least one analog position signal, an analog-to-digitalconverter receiving the at least one analog position signal andconverting the at least one position signal to a digital positionsignal, and a processing device determining a position of the movablemirror based on the digital position signal, wherein the movable mirrordevice is provided as a unitary device including the movable mirror, theposition sensor the analog-to-digital converter and the processingdevice.
 2. The movable mirror device of claim 1, wherein theanalog-to-digital converter is integrated in the processing device. 3.The device of claim 1, wherein the movable mirror comprises amicroelectromechanical system.
 4. The device of claim 1, wherein theposition sensor comprises a four quadrant diode and a light source toilluminate a backside of the movable mirror such that a reflection fromthe backside of the of the movable mirror falls on the four quadrantdiode.
 5. The device of claim 4, wherein the processing device furthercontrols a current supplying the light source.
 6. The device of claim 5,wherein the processing device comprises a flash memory, the flash memorystoring a target value of a sum signal from all quadrants of the fourquadrant diode, and controlling the current comprising obtaining acurrent sum signal and feeding the current sum signal and the target sumsignal to a controller of the processing device.
 7. The device of claim1, wherein the processing device comprising a stored lookup table totranslate the digital position signal to a position of the movablemirror.
 8. The device of claim 1, further comprising a digitalinterface, wherein the processing device transmits position informationvia the digital interface.
 9. The device of claim 1, wherein theprocessing device further transmits values of internal nodes of themovable mirror device via the digital interface.
 10. The device of claim9, wherein the values of internal nodes comprise one or more of anoutput value of the analog-to-digital converter, an output value of afilter, an output value of a dark current correction or non-normalizedposition data.
 11. The device of claim 1, further comprising a commandinterface to receive control commands.
 12. The device of claim 11,wherein the control commands comprise one or more of a sampling rate ofthe analog-to-digital converter, setting of internal coefficients,setting of a lookup table for position calculation, setting of a versionnumber, setting of an internal system variable, setting of a parameterof the movable mirror, an activation or deactivation of a currentregulation for a light source of the position sensor, and a selection ofinternal system nodes for transmission.
 13. The device of claim 11,wherein the command interface is a serial interface.
 14. The device ofclaim 1, further comprising a synchronization input, wherein theprocessing device synchronizes transmission of position informationbased on a signal of the synchronization input.
 15. A system,comprising: a movable mirror device, the movable mirror devicecomprising: a movable mirror, a position sensor measuring a position ofthe movable mirror and outputting at least one position signal, ananalog-to-digital converter converting an analog signal based on the atleast one position signal to a digital position signal, and a processingdevice determining a position of the movable mirror based on the digitalposition signal, wherein the movable mirror device is provided as aunitary device; and a target hardware coupled to the movable mirrordevice, the target hardware receiving position information indicating aposition of the movable mirror from the movable mirror device.
 16. Thesystem of claim 15, wherein the movable mirror device is coupled to thetarget hardware via at least one digital bus.
 17. The system of claim15, wherein the target hardware transmits a synchronization signal tothe movable mirror device.
 18. The system of claim 15, comprising aplurality of movable mirror devices coupled to the target hardware. 19.The system of claim 15, comprising a plurality of target hardwareentities coupled to the movable mirror device via a bus system.
 20. Alaser scanning microscope, comprising: a laser, a movable mirror device,the movable mirror device comprising: a movable mirror, a positionsensor measuring a position of the movable mirror and outputting atleast one position signal, an analog-to-digital converter converting ananalog signal based on the at least one position signal to a digitalposition signal, and a processing device determining a position of themovable mirror based on the digital position signal, wherein the movablemirror device is provided as a unitary device, the movable mirror devicebeing controllable to scan a sample with a laser beam generated by thelaser, and a light detector detecting light from the sample in responseto the sample being irradiated with the laser beam.